The present invention relates generally to the molding of the vehicle supporting elements formed of rubber and more particularly to an improved mold and method for producing rubber tracks as well as the resultant track produced by the mold.
Molded rubber tracks are in many cases being substituted for conventional metal tractor tracks. Rubber tractor tracks offer better maneuverability, better ride quality in rough fields, better flotation in wet fields, improved side hill stability, excellent traction, low maintenance and versatility compared to steel tractor tracks. Additionally, rubber tracks are being used with or even replacing conventional rubber tires on skid steer vehicles, tractors and other agricultural vehicles such as combines, trenchers, snow removers, spreaders, sprayers, wagons and carts, since rubber tracks are more friendly to agricultural fields, offer better flotation and less compaction than rubber tires, resulting in better crop yield. The use of rubber tractor tracks permits farmers to get out into the fields earlier in the planting season and plant more crops as compared to rubber tire equipped agricultural vehicles.
Rubber tractor tracks are defined by an endless rubber belt reinforced with continuous flexible steel cables bonded into the rubber. Presently, a complete rubber tractor track is molded flat in quarter sections, which are sequentially then bonded together during the curing process. In practice, the joint between the bonded-together sections tend to break in use. Additionally, the joint between the bonded-together ends is of a different cross-sectional dimension than the cross-sectional dimension of the major portion of the track length. Accordingly, during movement of the track-supported vehicle, the vehicle is subject to severe vibrations. Such vibrations are not only harmful to the vehicle, but also to pavement over which the vehicle is moved. Additionally, such vibration is annoying to the vehicle operator.
Another method involves building a complete track using a drum. Uncured or cured lugs are first manually clamped within pockets formed in the drum. Next, uncured rubber, calendered cord and wire cable are wrapped around the outside of the drum. Preformed uncured treads are then attached onto the uncured rubber. The drum is then disposed within an autoclave to cure the rubber and the parts attached thereto. The drum is then collapsed to remove the completed track. Since only low pressure can be applied the cured rubber is of a low density with resulting low strength. Also, the track lugs and treads are not generally integrally bonded to the rubber and are displaced during use.
Another method described is U.S. Pat. No. 6,086,811 teaches using an axially separatable two piece curing drum having a plurality of cavities centrally located on the peripheral surface of the drum for forming drive or guide lugs on the inner surface of the inner track. The guide lugs are centrally located and the drum is formed by two parts abutted at the centerline of the drum shown in FIG. 1.
This curing and method used for forming the track also has an outer tread forming segmented mold portion. Once the track is molded the outer segments radially expand outwardly and the curing drum with cured band can be removed and the fastening means holding the drum halves together are removed enabling the drum halves to be pulled apart thereby freeing the freshly molded track.
The prior art methods described above work well on the large tracked vehicles having the track mounted on axially spaced pairs of wheels. These tracks have the guide lugs arranged in a single row and positioned between the wheels and thus are readily adapted to the molding system described above in U.S. Pat. No. 6,086,811.
Smaller tracks used on small four wheeled vehicles such as skid steer loaders must employ other types of guide lugs or track restraining means to keep the track from coming off each pair of wheels. One such track has closely spaced guide lugs one each side of the track in circumferential alignment. Such tracks are sold commercially under the Goodyear brand name Trackman(copyright).
Due to the small size of these tracks the use of collapsible center segments is virtually impractical. The use of the split half curing drum as described in U.S. Pat. No. 6,086,811 is not possible due to the fact the guide lugs are positioned on the lateral ends or edges. Often this required a secondary attaching of guide lugs to be done with adhesives.
It is an object of the present invention to have a mold for tracked vehicles that does not require a radially collapsible core.
It is a further object to have two rows of guide lugs molded directly to the track band using a circular radial inner core.
An endless elastic track having guide lugs on the inner circumference and rubber tread lugs on the outer circumference and a thin continuous band extending in the circumferential directions is described. The thin band is circumferentially reinforced by substantially inextensible cords or bands. The track has a plurality of spaced rubber guide lugs. Each guide lug has an axial inner portion. The guide lugs are arranged in two rows. The first row of guide lugs is adjacent to the first lateral edge of the thin band and the second row of guide lugs is adjacent a second lateral edge of the thin band. The guide lugs for the first row are circumferentially offset relative to the guide lugs of the second row.
The guide lugs of the first row have no circumferential overlap relative to the guide lugs of the second row. The axial outer portion of the guide lugs are oriented substantially perpendicular to the circumferential direction. Each of the axial inner portions of the guide lugs can be inclined axially inwardly from a radially inner end toward the band.
The axially spaced distance S between the axially inner portions of the guide lugs of the first row and the second row at a location adjacent to the thin band is equal to or greater than the vehicle mount wheel width at the outer circumference of the wheels.
This elastic track having guide lugs on the inner circumference and rubber tread lugs on the outer circumference and a thin band continuously extending in the circumferential direction is produced by using an improved mold.
The improved mold has a radially outer molding portion for forming the tread lugs and a circular radially inner core for forming the guide lugs. The radial inner core has separable intermeshing first and second portions. Each first and second portion has a plurality of spaced spokes extending from a circular end. When the radially inner core has the first and second portions assembled and intermeshed, the spokes of the first portion are adjacent to the spokes of the second portion and the spokes of the first portion are spaced from the circular end of the second portion at the outer circumference of the radial inner core. The spokes of the second portion are also spaced from the circular end of the first portion at the outer circumference of the radial inner core. The spaces formed between the circular ends and the spokes formed guide lug cavities.
The spokes have an accurate circumferential outer surface having a radius of curvature R, R being the same as the radius of curvature of the circular ends. The spokes, in one embodiment preferably have a tapered end inclined axially outwardly and radially inwardly for forming the guide lugs with a thick base that narrows toward the tip. The spokes have axially extending sides in contact with the sides of the adjacent spokes of the opposite portion. The spokes are radially supported on one or both sides by an adjacent spoke of the opposite portion. The spokes of the first portion may have the ends radially supported by the circular end of the second portion while the spokes of the second portion may have the ends radially supported by the circular end of the first portion in one embodiment of the invention.
These and other features and advantages of the invention will become apparent from the following detailed description of the embodiments which taken in conjunction with the accompanied drawings illustrate by way of example the principles of the invention.
Definitions
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cCordxe2x80x9d means one of the reinforcement strands of which the plies in the track are comprised.
xe2x80x9cEquatorial plane (EP)xe2x80x9d means the plane perpendicular to the track""s axis of rotation and passing through the center of its tread.
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tread with a flat surface under load and pressure.
xe2x80x9cLateralxe2x80x9d and xe2x80x9claterallyxe2x80x9d means lines or directions that are parallel to the axis of rotation of the tire (also xe2x80x9caxialxe2x80x9d).
xe2x80x9cPly,xe2x80x9d means a continuous layer of rubber-coated parallel cords.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d means directions extending radially toward or away from the axis of rotation of the track.
xe2x80x9cZero-degree wiresxe2x80x9d means at least one layer of parallel cords andusually metal wire), underlying the tread, unanchored to the bead, spiraling circumferentially around the tread, and having cord angles in the range from 0 degrees to 5 degrees with respect to the equatorial plane of the tire.